Phototransitional environments are what I encounter most - not quite in the dark, but not fully lit either:
Shadows are really good to hide in from a distance, but they lose their effectiveness the closer to an observer you are. Multiple light sources (streetlights, neon signs, billboards, etc) project overlapping shadows making it more difficult to find true darkness. Most objects project 2 shadows - the 'umbra' (the darkest part where shadows overlap) and one or two 'penumbras' where one shadow is partially illuminated by an opposing light source.
Positioning is key in blending into shadows and not silhouetting yourself -even if you're in the deepest darkest shadow, if you're standing upright against a bright surface you'll still stand out like dog's balls. Pressing yourself up against an object or lying prone will make your silhouette stick out less.
Position yourself according to where the most likely observers can see you from; doorways, windows, balconies, vehicles, etc. When moving from one shadow to another, note how deep & dark they look from a distance - if anyone tries to spot you in there from the same distance, you'll have a general idea of how visible you'll be. That being said, even up close in the right conditions you'll still be very hard to make out. I recall a moment on our first op during NOPCON 1 where we were moving along a street, dashing from shadow to shadow wearing a mix of woodland camouflage & solid black. Ghost was wearing solid black and jumped into the shadow of a shrub - the darkness hid him so well that I damn near jumped right into him. If it weren't for the eye slit in his balaclava, I would never have noticed him - and he was right in front of me.
Different environments cast different 'patterns' of shadows - on a rural street, for example, there are large blobs of darkness between streetlights, whereas in more urban settings the shadows are more tight with increased streetlight frequency and more obstacles (front yards, alleyways, cars, etc). Sometimes light is shining through a medium such as tree branches or a construction sight, scattering the light and casting 'patterns' on the ground. These can still be used to disguise your form to a casual observer. If you're wearing solid black and are in an environment with long, straight shadows, you can even hide in the light by mimicking the pattern of shadows around you.
Of course a shadow is just a shadow until it moves. If the shadows are thick enough, you can move along them slowly enough that you won't be immediately visible, but if a blob of darkness suddenly moves along on its own then that's immediately suspicious. Of course shadows move on their own under the right circumstances, such as vehicles & trains passing by with their lights on or flashing billboards. You can use this mobile light pollution to disguise your own movements, just like moving amongst shrubbery during a strong wind. In both these instances it will also mask the sound of your movement too.